The invention relates to a liner for use in a water cooled monolithic electroslag remelting mold. More specifically it is directed to a mold liner composed of copper or a copper alloy having physical characteristics which reduce thermal creep distortion in the liner structure and simultaneously increase the cooling effect provided by the coolant circulating behind the liner.
The electroslag remelting process essentially comprises the fusing of metal from a consumable electrode under a blanket of molten slag. This is generally accomplished by suspending a consumable electrode having the composition of metal desired within a water cooled copper or steel mold and introducing molten slag into the mold, the slag acting as the conductor for the electric current passing between the consumable electrode and the base plate, stool or starter plate. The current passing through the electrode in the molten slag heats the electrode and droplets of metal fuse off of its lower end and fall through the slag to the bottom of the mold where a pool of molten metal forms and solidifies upwardly from the bottom of the pool. A refining action takes place in the molten metal as it passes through the molten slag and, as the electrode is progressively consumed, refined metal builds up from the bottom of the mold to form an ingot. The molten slag floats on the pool of refined metal and is maintained in contact with the lower end of the consumable electrode. The refining process continues until the electrode is consumed or substantially consumed. Thereafter the ingot is removed from the mold.
As the slag rises in the mold, it is desirable that it form a relatively thin layer of solidified slag along the interior surfaces of the mold. It is common practice for molds used in the electroslag refining process to be water cooled and it has been found desirable that the interior lining of the mold be composed of copper because of its relatively high constant of specific heat conductivity. However, in the high temperature environment of the electroslag refining process, it has been found that copper liners have a tendency to creep thus becoming distorted and shortening their useful life. At the same time the danger of incursion of water into the molten slag is increased which, in turn, may cause hydrogen embrittlement in the resulting product. Further, the uniform quality of the ingot obtained by the process is affected by the temperature of the mold and an uneven cooling produces thermal creep with a resulting inferior quality of the steel. In addition, the non-uniformity of dimensions within the mold due to thermal creep may cause difficulty in the subsequent dislodging of the ingot from the mold.